Cyclohexanol and alkanols for example ethanol, represent important chemicals and organic solvents in the organic chemical industry.
Cyclohexanol is mainly used in a dehydrogenation for producing cyclohexanone, while cyclohexanone represents a main intermediate for further producing nylon 6 and nylon 66. Since the birth of nylon, big chemical companies all around the world have been dedicated to identifying an industrial source for cyclohexanol or cyclohexanone. In 1980s, the Japan asahi kasei company developed a process for producing cyclohexanol by hydration of cyclohexene (cyclohexene hydration process). However, the process suffers from the following problems: (1) the direct hydration of cyclohexene is thermodynamically restricted, and cyclohexene is only slightly soluble in water, for this reason, the hydration reaction mainly occurs at the interface between the two phases, causing the cyclohexene hydration reaction to proceed at a rather slow speed with a low single-pass conversion; Even if a supersiliceous ZSM-5 catalyst is used, and two slurry reactors in series are used with a residence time of 2 h, the single-pass conversion of cyclohexene reaches merely 12.5%; Such a low single-pass conversion necessitates separation of a massive amount of unreacted cyclohexene from the product stream and recycling of same, which results in huge energy consumption; (2) cyclohexene with a high purity should be used as the feed stock, otherwise the dilution by other components will result in more amount of mass to be recycled and more lowered reaction efficiency; Cyclohexene is produced from a partial hydrogenation of benzene, whose product stream contains a significantly amount of cyclohexane and benzene other than cyclohexene. The boiling point of the three is much close to one another, and therefore purification of cyclohexene is much difficult, which necessarily renders much higher purification cost; (3) the process involves a complicate reaction system consisted of an aqueous phase, an oil phase and a solid catalyst phase, which necessitates strong stirring for the formation of an emulsion system throughout which aqueous droplets and oil droplets are sufficiently dispersed, so as for cyclohexene to be adsorbed onto the surface of the catalyst, and also necessitates well separation of the catalyst from the oil phase at the sedimentation section, all of which complicate the operation, and lead to severe loss of the catalyst.
Ethanol has been produced on an industrial scale mainly by the direct ethylene hydration method, while for some countries with plentiful agricultural by-products, the fermentation method prevails as the process for producing ethanol. The fermentation method suffers from the problem of severe pollution, and further, is criticized for food consumption, and therefore is not suitable for a country with a huge population and less arable land. The direct ethylene hydration method is rather demanding in terms of reaction conditions, which needs elevated temperatures and high pressures. Further, the price of ethylene is much influenced by the international oil price fluctuations, and for a country lacking of oil resources, the direct ethylene hydration method for producing ethanol has to face some cost pressure.
Therefore, there is still a need in the prior art for a process for producing cyclohexanol, especially a process for co-producing cyclohexanol and alkanol (for example ethanol), which is capable of co-producing cyclohexanol and alkanol (for example ethanol) with a more simplified production procedure and at a relatively lowered production cost, and further overcoming the problems associated with the prior art.